What causes the mysterious light of sonoluminescence?

The answer

Sonoluminescence occurs when sound waves cause gas bubbles in liquid to implode so rapidly they emit brief flashes of light. First observed in 1934 by H. Frenzel and H. Schultes at the University of Cologne, single-bubble sonoluminescence was reliably produced in 1989 by Felipe Gaitan. During acoustic cavitation, a bubble expands then collapses in microseconds, compressing its contents to temperatures exceeding 20,000 Kelvin - hotter than the Sun's surface - and pressures of thousands of atmospheres. The light pulses last merely 35-350 picoseconds. The exact mechanism remains debated: proposed explanations include thermal bremsstrahlung radiation, quantum vacuum effects, and plasma formation. The phenomenon has been studied for potential applications in medical imaging, chemical catalysis through sonochemistry, and as a model for inertial confinement fusion dynamics.